The invention relates to concentrated, aqueous-alcoholic, low-viscosity, clear, relatively colourless solutions which are stable over a temperature range of between 5 and 50xc2x0 C. and which contain at least 50% by weight of alkylamido-propylbetaine corresponding to the general formula (I): 
in which R1 represents the alkyl radical of a natural fraction of fatty acids of coconut or palm oil type, which are, approximately, saturated fatty acids with about 40-50% of lauric acid and 15-20% of myristic acid (in the account hereinbelow this will be referred to simply as betaine). The solutions have these qualities only if their composition is chosen precisely in a region of the betaine/ethanol/water diagram standardized to 100 on a weight basis after correction of the NaCl present.
Betaines corresponding to the general formula (I) are amphoteric surfactants that are very well tolerated by the skin, they have excellent cleansing and foaming properties and are entirely suitable for making a whole range of surfactant compositions, such as washing agents, cleansing agents (liquid products for washing up by hand), haircare compositions (shampoos) and bodycare compositions (shower gels and bubble baths) .
The preparation of this type of betaine is described in many documents, and the processes are known to those skilled in the art, for example U.S. Pat. No. 3,225,074 (American Cyanamid). It consists in reacting a fatty acid or a fatty acid fraction with N,N-dimethyl-1,3-propanediamine (DMAPA) between 140 and 200xc2x0 C., and then in quaternizing the tertiary amidoamine obtained, of general formula (II): 
with monochloroacetic acid in the presence of an alkaline salt or the corresponding salt of this acid, the quaternization reaction usually taking place in aqueous medium. The alkaline chloride, which is often sodium chloride, obtained as a by-product in the reaction, is generally left in this aqueous betaine solution. These aqueous betaines are sold at a concentration in the region of 30% by weight.
Attempts have often been made to prepare industrially betaine solutions that are as concentrated and as fluid as possible, for quite understandable reasons of reducing the transportation and storage costs, without, however, sacrificing the ease of their handling.
A person skilled in the art knows that when the concentration of an aqueous surfactant solution increases, its viscosity also increases. Nevertheless, certain authors have sought to concentrate, by evaporation under reduced pressure, betaine solutions obtained according to the usual processes, but their viscosity increases rapidly and they become pasty at about 40xc2x0 C. by weight of betaine, then continue to solidify as water is removed therefrom; it is not possible to obtain concentrated solutions via this route. However, it is reported in EP 0,302,329 (Th. Goldschmidt) that it was possible partially to circumvent this difficulty by adjusting the pH of the solution to between 1 and 4.5 with an inorganic acid (hydrochloric, sulphuric or phosphoric acid). The authors thus obtained solutions containing 43 to 44% by weight of betaine (or 53 to 54% solids) with a viscosity in the region of 1000 mPa.s at 25xc2x0 C. However, the problems of corrosion during storage and transportation, along with the atypical pH of these betaine solutions, limit their use and, moreover, they gel below 16xc2x0 C.
Another route is that for obtaining betaine in powder form, by spraying fluid solutions at less than 30%. It may be thought to redissolve these powders in suitable solvents, but redissolving these powders is hampered by the formation, when the powder is placed in contact with the solvent, of lumps or gelled pastes which are virtually impossible to redissolve, or at least not within reasonable times that are compatible with industrial activity.
International patent application WO 95/12856 (Henkel) discloses and claims a process for manufacturing surfactants of betaine type with a low salt content (0.98 to 1.01% residual NaCl) by quaternization of tertiary amines and/or tertiary amidoamines with sodium monochloroacetate in an aqueous-alcoholic mixture composed of 5 to 10% by weight of water and 35 to 50% by weight of ethanol and/or isopropanol, this reaction being followed by removal of the salt fraction precipitated, total removal of the solvent and readjustment of the water in the reaction medium in order to bring the solution to the desired active material concentration xe2x80x94in this case 30%. The water/ethanol weight ratio claimed by the authors is typical for a process aimed at removing the NaCl formed during the reaction. A composition of this type formed the subject of U.S. Pat. No. 4,705,893 (KAO), represented by a pentagonal zone of the betaine/water/ethanol ternary diagram defined by the triangular coordinates (80/10/10), (80/15/5), (40/55/5), (40/27.5/32.5) and (52.5/10/37.5). Both of these cases involve processes whose essential aim is to obtain totally aqueous non-concentrated amphoteric surfactant solutions with low salt contents.
A person skilled in the art is familiar with the idea of the possible existence of domains of fluid phases in an amphoteric surfactant/water/solvent system. This idea is pursued in WO 95/14076 (Albright and Wilson), in reality without any concrete teaching other than that of the individual examples reported in that publication, which come closest to the conditions of the present problem, namely, compositions of cocoor lauryl-amidopropylbetainexe2x80x94salt dissolved in a mixed solvent of water/glycol type.
The problem which still remains is to obtain solutions of coconut or palm oil alkylbetaine which are as concentrated as possible, i.e. at least 50% by weight, clear and relatively colourless, fluid and pumpable (viscosity of less than 1000 mPa.s), stable between 5 and 50xc2x0 C. for prolonged periods, in order to reduce the packaging, transportation and storage costs, readily manipulable, and which can be formulated in their given state with other surfactants, for example alkyl ether sulphates, alkanolamides or other starting materials forming part, in particular, of the formulations for liquid soaps, shampoos, shower gels and other cosmetic preparations.
The present invention provides a solution to this technical problem, which consists in preparing the alkylbetaine in the presence of small amounts of ethanol, provided that, however, the system remains limited to a quite precise and narrow region of the phase diagram as will now be defined.
The reckoning is determined on betaine/water/ethanol ternary compositions, represented on the ternary diagram in reduced coordinates
B*=[betaine/(betaine+water+ethanol)]xc2x7102 
W*=[(water/(betaine+water+ethanol)]xc2x7102 
E*=[ethanol/(betaine+water+ethanol)]xc2x7102 where betaine has the sense of, and is measured as, betaine=solidsxe2x88x92NaCl, in which the 100% loop relationship applies for the composition B*+W*+E*=100, all of the betaine, solids, water, ethanol and NaCl magnitudes being expressed on a weight basis, the reduced magnitudes B*, W* and E* appearing as weight %.
With this definition, the betaine considered is a raw betaine, i.e. one consisting of alkylamidobetaine as corresponds to formula I, with a few reactant residues and a few reaction by-products not exceeding 3% by weight (see Example 1).
The compositions of the invention are those which obey the following relationships
55%xe2x89xa6B*xe2x89xa662%
E*xe2x89xa721%
37%xe2x89xa6W*/W*+E*xe2x89xa650%
In the compositions of the invention, NaCl is present to a maximum level of 4.5% by weight, beyond which value these compositions become uncontrollable, if only by precipitation of the salt.
The compositions according to the invention are capable of prolonged storage over periods of at least three months, in the course of which no gelling, demixing, precipitation of salts or appreciable change in colour or clarity is observed in the temperature range between 5 and 50xc2x0 C. These solutions also have the advantage of being relatively non-foaming in the concentrated state, which makes them easier to manipulate. Another advantage lies in the fact that these concentrated solutions are sufficiently resistant to microbial invasion, such that it is unnecessary to add preserving agents. These characteristics make these solutions particularly suitable for making cosmetic compositions.
Another subject of the present invention relates to the process for manufacturing these concentrated solutions, which consists in preparing the intermediate coconut or palm oil dimethylamidopropylamides and in quaternizing them with monochloroacetic acid in the presence of sodium hydroxide or sodium monochloroacetate directly in the solvent medium chosen, i.e. obeying the composition rule
E*xe2x89xa721%
37%xe2x89xa6W*/W*+E*xe2x89xa650%
defined above.